The present invention relates to railcar truck assemblies and more specifically to squaring of three-piece railcar truck assemblies.
In previous railcar truck assemblies, wide laterally-extending stop surfaces or lands adjacent to the side frame wear plates and bolster friction shoe pockets have been provided to avoid rotation of the bolster about its longitudinal axis, that is, bolster rotation. Alternatively, bolster rotation stop lugs have been provided at the inboard face of a side frame column to inhibit rotation of the bolster in the side frame about the bolster's longitudinal axis. Such rotation about the bolster's longitudinal axis is known as pitching.
The bolster may also rotate about a vertical axis. Such rotation of the bolster is known as warping or lozenging. When the truck warps, it is unsquare: the side frames operationally remain parallel to each other, but one side frame moves slightly ahead of the other in a cyclic fashion. In truck warping, the bolster rotates about its central vertical axis, causing angular displacement of the side frame and bolster longitudinal axes from a normal relationship. Warping results in wheel misalignment with respect to the track. It is more pronounced in curved track and usually provides the opportunity for a large angle-of-attack to occur. Warping can lead to railcar truck hunting, that is, a continuous instability of a railcar wheel set wherein the truck weaves down the track in an oscillatory fashion, usually with the wheel flanges striking against the rail.
To reduce truck warping, U.S. patent application Ser. No. 08/950,178, filed on May 2, 1997 and entitled "Improved Bolster Land Arrangement for Railcar Truck", discloses that the free travel between the mated bolster and side frames at the side frame columns may be constrained. The clearance or separation gap between the bolster lands and the side frame columns is reduced.
However, in some environments, it may be desirable to avoid using a tight clearance between the bolster lands and side frame columns to reduce warping. For example, in some environments, it may be desirable to provide closely-spaced surfaces to reduce warping that can be more easily inspected for wear than at the bolster lands, or it may be desirable to provide design alternatives to closely-spaced surfaces at the bolster and side frame lands.